Mechanisms of endotoxin-induced NO, IL-6, and TNF-α production in activated rat hepatic stellate cells: Role of p38 MAPK

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Abstract
Compelling experimental evidence indicates that the interactions between endotoxin and hepatic stellate cells (HSCs) can play a significant role in the pathogenesis of liver disease. Endotoxin-induced release of a multifunctional mediator NO (via inducible NO synthase) and the proinflammatory cytokines tumor necrosis factor α (TNF-α) and interleukin (IL)-6 by HSCs could be an important mechanism of pathological changes in the liver. However, the signaling mechanisms of these effects are poorly understood. In this study, we found that endotoxin causes activation of mitogen-activated protein kinases (MAPKs) (extracellular signal-regulated protein kinase [ERK] 1 and 2, p38, and c-Jun NH2-terminal kinase [JNK]) and nuclear factor κB (NF-κB) and production of H2O2 in culture-activated HSCs. However, only p38 and NF-κB were found to be responsible for the synthesis of NO, IL-6, and TNF-α. Exogenous H2O2 caused modest stimulation of TNF-α synthesis, did not affect the synthesis of NO or IL-6, and did not activate NF-κB or MAPKs. Inhibition of p38 and NF-κB activation by SB203580 and pyrrolidine dithiocarbamate, respectively, blocked endotoxin-induced H2O2, NO, TNF-α, and IL-6 synthesis. Inhibition of ERK1/2 and JNK phosphorylation did not alter these effects of endotoxin. Whereas SB203580 inhibited endotoxin-induced NF-κB activation, pyrrolidine dithiocarbamate did not affect p38 phosphorylation in endotoxin-stimulated cells. In conclusion , endotoxin-induced synthesis of NO, TNF-α, and IL-6 in HSCs is mediated by p38 and NF-κB, with involvement of H2O2 in TNF-α production. Supplementary material for this article can be found on the HEPATOLOGY website (http://interscience.wiley.com/jpages/0270-9139/suppmat/index.html).